Protein import and export across the bacterial outer membrane.

The bacterial outer membrane forms an impermeable barrier to the environment, but a wide variety of substances must cross it without compromising the membrane. Perhaps, the most fascinating transport phenomenon is the import and export of very large protein toxins using relatively small β-barrel proteins residing in the outer membrane. Progress has been made on three systems in recent years that shed light on this process. In this review, we summarize bacteriocin (toxin) import using TonB-dependent transporters and protein secretion by autotransporters and two partner secretion systems. Published by Elsevier Ltd.